Method for making stabilised polyamide compositions

ABSTRACT

The invention relates to a process for preparing stabilized compositions based on polyamide. The stabilizer is a phosphorus stabilizer selected from phosphorous acid and hypophosphorous acid. It is introduced before or during the polymerization of the polyamide. The use of these stabilizers prevents foaming phenomena.

[0001] The invention relates to a process for preparing stabilizedcompositions based on polyamide and to the compositions obtainable bythe process. The compositions of the invention may in particular be usedfor preparing synthetic yarns, fibres and filaments.

[0002] Polyamide is a synthetic polymer widely used for preparing yarns,fibres and filaments. These fibres, yarns and filaments are subsequentlyused to produce fabrics, and in particular dyed fabrics.

[0003] The polyamide may undergo degradation when subjected to elementsor external conditions such as UV radiation, heat or inclement weather.Degradation may also be induced by the heat used during its preparationand/or shaping. This instability is manifested in instances ofdegradation, loss of mechanical properties, and colour changes. For someapplications, these problems may become critical.

[0004] In order to enhance the stability of polyamides it is known tocombine them with additives. Numerous additives are sold for thispurpose. They are frequently classed according to their method ofaction: anti-oxidant, anti-UV, UV absorbers, etc.

[0005] In order to stabilize the polyamide, known antioxidants includein particular those containing hindered phenol units, phosphorusstabilizers, and light stabilizers containing at least one hinderedamine unit.

[0006] For the stabilization, known phosphites include phosphitessubstituted by alkyl and/or aryl radicals, for exampletris(2,4-di-tert-butylphenyl) phosphite. These stabilizers, whenintroduced into the polyamide preparation medium, cause severe foaming,which carries the risk of impairing the plant and the products produced.This severe foaming occurs even in the presence of conventionalantifoams. To prevent this problem, the document WO 9418364 teaches, forexample, introducing these stabilizers by mixing, in the melt state, thepolyamide and a masterbatch of the stabilizer in a polyamide matrix.

[0007] Foaming problems may also be encountered with other stabilizingadditives.

[0008] For various technical/economic reasons it is often preferred tointroduce additives into a polymer other than by mixing in the meltstate. Accordingly, it is often preferred to introduce these additivesinto the polymer synthesis medium before the polymerization is carriedout. This method of introduction is generally referred to by the term“introduction during synthesis”. Such a method makes it possible, amongother things, to obtain very good dispersion of the additives in thepolymer and sometimes to prevent polymer remelting operations. Moreover,the introduction of stabilizers during synthesis prevents instances ofdegradation during the preparation of the polyamide and/or its shaping.

[0009] It is an object of the invention to provide a process forpreparing a stabilized composition based on polyamide, comprising aphosphorus-based additive introduced during synthesis.

[0010] The invention accordingly provides a process for preparing astabilized composition based on polyamide, comprising a phosphorusstabilizer additive, characterized in that the phosphorus stabilizeradditive is selected from phosphorous acid and hypophosphorous acid andin that it is introduced into the polyamide polymerization medium beforeor during the polymerization phase. Its proportion by weight in thecomposition is preferably between 0.01% and 0.04%.

[0011] In one preferred embodiment, it is possible to use at least oneother stabilizer additive introduced into the polyamide polymerizationmedium before or during the polymerization phase. The additionaladditive is selected from hindered phenol antioxidants and lightstabilizers containing at least one hindered amine unit (hindered aminelight stabilizers, HALS). It is also possible to use a combination ofthese two additives with the phosphorus stabilizer. The presence of thephosphorus stabilizer selected from phosphorous acid and hypophosphorousacid additionally reduces the foaming due to the further individualadditives.

[0012] The light stabilizers containing at least one hindered amine unitenhance the light stability of the polyamide and prevent a loss ofcolour brightness when the polyamide is dyed or comprises colourpigments.

[0013] The process for preparing polyamide according to the inventionmay be selected from all known processes with the proviso that thephosphorus stabilizer, and where appropriate the other stabilizeradditives, are introduced into the polymerization medium before thepolymerization phase has properly started. It is possible for a producthaving a low degree of polycondensation to be formed before theadditives are introduced.

[0014] Where two or more stabilizer additives are used, they may beintroduced into the polymerization medium either in succession, atdifferent stages of the process before the polymerization phase, or atthe same time.

[0015] The light stabilizer containing at least one hindered amine unitis preferably selected from 4-amino-2,2,6,6-tetramethylpiperidine,4-carboxy-2,2,6,6-tetramethylpiperidine, aromatic compounds of formula(I) containing two or three carbonyl functions and including at leastone group containing a hindered amine unit, the said unit being part ofa group attached to one of the carbonyl functions. The carbonyl functionmay be part of an amide, ester or ester-amide group.

[0016] in which p is 0 or 1 and R1 and R2 are identical or differentgroups of which at least one contains a hindered amine unit.

[0017] Where p is 0, the additive may have a chemical structure (II) or(III), defined as follows:

[0018] in which R1 and R2 are identical or different groups of which atleast one contains a hindered amine unit, a group not containing asterically hindered amine unit which may be selected from C₁ to C₁₈alkoxy; aminoalkyl optionally substituted by halogen, C₁ to C₅ alkoxy,carbonyl groups, carbamyl groups or alkoxycarbonyl groups; and C₃ to C₅epoxides;

[0019] the group or groups containing a sterically hindered amine unitmay be selected from the following compounds of formula (IV):

[0020] in which R and R′ are selected independently from hydrogen, C₁ toC₁₂ alkyl, C₁ to C₈ alkoxy, groups of structure —COR3, where R3 isselected from hydrogen and C₁ to C₆ alkyl; phenyl; the group —COO(C₁ toC₄ alkyl); the group of structure NR5R6, where R5 and R6 are selectedindependently from hydrogen, C₁ to C₁₂ alkyl, C₅ or C₆ cycloalkyl,phenyl, alkylphenyl in which the alkyl is from C₁ to C₁₂, or R5 and R6form, with the nitrogen atom to which they are bonded, a ring of 5 to 7atoms optionally including an oxygen atom or another nitrogen atom,preferably forming a group from the class of the piperidines ormorpholines.

[0021] One preferred compound for the light stabilizer is the compoundof formula (V):

[0022] in which R′₂ is selected from C₁ to C₂₀ alkyl, C₁ to C₂₀aminoalkyl, C₁ to C₂₀ substituted aminoalkyl, C₁ to C₂₀ hydroxyalkyl, C₁to C₂₀ alkene, C₁ to C₂₀ substituted alkene, alkoxyalkyl groups,C₁₋₂₀-oxy-N—C₁₋₂₀-alkyl groups, C₁ to C₁₀—N-cycloalkyl groups, C₁ toC₁₀—N-cycloalkyl groups substituted by a group —COR4 where R4 isselected from hydrogen, C₁ to C₆ alkyl, phenyl, groups C₁₋₂₀COO(H orC₁₋₄ alkyl) and in which R′ is as defined for the formula (IV).

[0023] The light stabilizer is more preferably still the compound offormula (VI)

[0024] This additive is supplied, for example, by Clariant under thename Nylostab S-EED.

[0025] The proportion in the composition of the light stabilizeradditive is advantageously between 0.15% and 0.5% by weight.

[0026] The light stabilizer of formula (VI) is preferably introducedinto the polymerization medium in the form of a suspension or a solutionin water, caprolactam, or a water/caprolactam mixture. The concentrationby weight in the solution or in the suspension may, for example, bebetween 5% and 50%. Preference is given to using a mixture ofcaprolactam and water containing more caprolactam than water. The formof introduction, suspension or solution, may depend in part on thetemperature and pressure conditions at the time of introduction.

[0027] The antioxidant is preferably selected from alkylatedmonophenols, alkylated hydroxyquinones, alkylidenebisphenols, benzylcompounds with alkyl hindrance, acylaminophenols, and esters of□-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid. Mention is made inparticular of1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene,supplied for example by CIBA under the name IRGANOX 1330, andN,N′-hexamethylene bis(3,5-di-tert-butyl4-hydroxyhydrocinnamamide),supplied for example by CIBA under the name IRGANOX 1098.

[0028] The proportion of the second additive in the composition isadvantageously between 0.10% and 0.30% by weight.

[0029] The stabilized composition based on polyamide may comprise otheradditives in addition to the additives already mentioned. Theseadditives may be introduced by mixing them into the polymerizationmedium or by mixing them in the melt phase. By way of example of suchadditives, mention is made of pigments or delustrants intended to givethe compositions a matt and/or coloured appearance, flame retardants,and other stabilizers.

[0030] In one particular embodiment of the invention, the compositionscomprise a delustrant in the form of particles based on titanium dioxideor zinc sulphide. The concentration of particles in the composition maybe between 0.01% and 3% by weight. It is advantageously greater than 1%.The delustrant is preferably introduced into the polymerization mediumbefore or during the polymerization phase. In this embodiment, theparticles are advantageously introduced in the form of an aqueoussuspension. The particles based on titanium dioxide are advantageouslycoated. The coating in question may comprise, for example, asilica-based coating with, where appropriate, alumina and/or a manganeseoxide.

[0031] The composition prepared by the process of the invention may bebased on a polyamide of the type obtained by polymerization from alactam and/or an amino acid, or based on a polyamide of the typeobtained by polycondensation of a dicarboxylic acid and a diamine. Thecompositions are preferably based on polyamide 6, polyamide 66, andblends and copolymers based on these polyamides. It may in particularcomprise a polyamide 6,6/6 copolymer when use is made of a stabilizer offormula (VI) introduced into the polymerization medium in the form of asolution or dispersion in a liquid comprising caprolactam.

[0032] In one particular embodiment, the composition is based onpolyamide 6,6. One advantageous preparation process starts from ahexamethylenediammonium adipate salt, preferably in the form of asolution at salt concentrations of between 50 and 70% by weight. Thisprocess, continuous or batchwise, comprises a first phase of waterevaporation and a second phase of polymerization by polycondensation.

[0033] The compositions may be shaped into yarns, fibres and filaments,directly after polymerization, without intervening steps ofsolidification and remelting. They may also be shaped into granules,intended for remelting for later definitive shaping, for example for theproduction of moulded articles or for the production of yarns, fibres orfilaments.

[0034] The yarns, fibres and filaments shaped from compositions obtainedby the process of the invention are produced by melt spinning: thecomposition is extruded in the melt state through dies comprising one ormore orifices.

[0035] All techniques of melt spinning may be used. The filaments may bedrawn or drafted, in the form of a multifilament yarn or a roving, inone continuous step or intermittently, and may undergo varioustreatments: sizing, texturing, setting, etc.

[0036] For the production of multifilament yarns, mention is made inparticular of high-speed spinning processes, at spinning speeds of morethan 3 500 m/min. Such processes are often designated by the followingterms: POY (partially oriented yarn), FOY (fully oriented yarn), and SDY(spindraw yarn). These yarns may further be textured, depending on theirintended use. The yarns obtained by these processes are especiallysuitable for the production of woven or knitted fabrics.

[0037] To produce fibres, the filaments may, for example, be broughttogether in sliver or web form, directly after spinning orintermittently, drawn, textured and cut. The fibres obtained may be usedto produce nonwovens or spun yarns.

[0038] The compositions may also be used for the production of flocktow.

[0039] The yarns, fibres and filaments, and the articles obtained fromthe yarns, fibres and filaments, may be dyed. Mention is made inparticular of bath-dyeing or jet-dyeing processes. The preferred dyeingsare acid, metallized or non-metallized dyeings.

[0040] The compositions of the invention allow articles to be obtainedwhose colour fastness with respect to light is excellent. They also makeit possible to obtain improved fastness of the dyeing to washing.

[0041] Further details and advantages of the invention will appear moreclearly on viewing the examples given below solely by way of indication.

EXAMPLE 1

[0042] A copolymer based on polyamide 66 is prepared from 3 590 kg of anaqueous hexamethylenediammonium adipate salt solution with aconcentration of 62% by weight, to which the following are added:

[0043] 3 940 g of a 25% aqueous acetic acid solution

[0044] 1 000 g of a 40% aqueous phosphorous acid solution

[0045] 300 g of Rhodia Silcolapse 5020 antifoam

[0046] a dispersion by mixing 40 l of caprolactam, 10 l of water, 6 kgof Nylostab SEED sold by Clariant, 3 kg of Irganox 1098 sold by Ciba.

[0047] The polyamide is prepared according to a standard processcomprising a step of concentrating this solution in an evaporator, astep of polycondensation in a stirred autoclave reactor, with adistillation phase of approximately 45 minutes at a pressure plateau of1.85 MPa for which the final temperature is 245° C., a decompressionphase of approximately 35 minutes from 1.85 MPa to 0.1 MPa at a finaltemperature of 260° C., and a finishing phase of approximately 30minutes for which the final temperature is 270° C.

[0048] During the distillation phase under pressure, after 6 minutes,128 kg of a 25% by weight aqueous dispersion of coated titanium dioxideparticles are added.

[0049] No foaming is observed during the decompression phase. Acopolymer based on polyamide 6,6 is obtained, containing 2.0% by weightof polyamide 6 units and 1.6% of titanium dioxide.

[0050] The copolyamide is spun by a spindraw process. The winding speedis 4 500 m/min. The linear density of the yarns obtained is 78 dtex per68 filaments. The tenacity of the yarn is 42 cN/tex and the elongationat break is 38%.

[0051] A knitted fabric is produced from the yarns. The fabric is washedat 60° C. for 20 minutes in the presence of a detergent compositioncomposed of 2 g/l of Sandozine MRN sold by Clariant, 2 g/l of Sirrix ARand 2 g/l of sodium carbonate. The fabric is then heat-set at 190° C.for 45 seconds.

[0052] The fabric is dyed by immersion at 98° C. for 45 minutes at a pHof 6 in the presence of the following:

[0053] dyes sold by Ciba

[0054] 0.0247% by weight of Irgalan yellow 3 RV 250%

[0055] 0.0170% by weight of Irgalan bordeaux EL 200%

[0056] 0.2220% by weight of Irgalan grey 200%

[0057] 2% by weight of a levelling agent, C14 sold by CHT

[0058] 0.5 g/l of sodium acetate

[0059] The light fastness of the fabric was tested using a Xenotest 450apparatus in accordance with the standard DIN 75202 over 4 cycles (FAKRAtest). After 4 cycles, the rating is 6-7.

EXAMPLE 2 Comparative

[0060] A copolyamide is prepared by the process of Example 1, withoutadditives. The rating is 5.

EXAMPLE 3

[0061] Compositions based on polyamide 6,6 were prepared in a 300 mlreactor equipped with a window allowing any foaming to be observed. Thepolyamide is prepared from a hexamethylenediammonium adipate salt insolution by a process similar to that of Example 1. The decompressionphase is carried out in 10 minutes so as to be implemented underconditions similar to the conditions of Example 1 as regards thesensitivity to foaming. During the preparation, additives are added:

[0062] coated titanium dioxide particles (1.6% by weight relative to thecomposition obtained). The particles are added 5 minutes after thebeginning of the plateau at 1.85 MPa.

[0063] Phosphorous acid in solution: added to the solution of thehexamethylenediammonium adipate salt

[0064] Nylostab SEED sold by Clariant, Irganox 1098, Irgafos 168(phosphorus stabilizer), Irgafos 12 (phosphorus stabilizer), sold byCiba. These products are introduced into the melted caprolactam at 150°C. during the decompression phase.

[0065] A variety of additives are tested, and also differentcombinations. The results are set out in Table 1. TABLE 1 Level ofIrganox 198 Irgafos 168 Irgafos 12 H₃PO₃ Nylostab foaming 0.15% / / / /1 / 0.15% / / / 1 / / / / 0.3% 1 0.15% / 0.15% / 0.3% 3 0.15% / / 0.02%0.3% 0

[0066] The amounts of additives are expressed by weight relative to thecomposition obtained. The level of foaming is evaluated by the height ofthe foam in the reactor: 0 for zero foaming, 3 for extensive foaming.

[0067] It is observed that the phosphorous acid inhibits the foaminginduced by the presence of the other additives.

1. Process for preparing a stabilized composition based on polyamide,comprising a phosphorus stabilizer additive, characterized in that thephosphorus stabilizer additive is selected from phosphorous acid andhypophosphorous acid and in that it is introduced into the polyamidepolymerization medium before or during the polymerization phase. 2.Process according to claim 1, characterized in that the compositioncomprises at least one other stabilizer additive introduced into thepolyamide polymerization medium before or during the polymerizationphase, selected from hindered phenol antioxidants and light stabilizerscontaining at least one hindered amine unit.
 3. Process according toeither of the preceding claims, characterized in that the compositioncomprises as other stabilizer additive: an antioxidant selected fromalkylated monophenols, alkylated hydroxyquinones, alkylidene bisphenols,benzyl compounds with alkyl hindrance, acylaminophenols, and esters of□-(3,5-di-tert-butyl-4-hydoxyphenyl)propionic acid and/or a lightstabilizer containing at least one hindered amine unit and selected fromaromatic compounds containing two or three carbonyl functions to whichat least one sterically hindered amine unit is attached, the said unitbeing part of a group attached to one of the carbonyl functions,4-amino-2,2,6,6-tetramethylpiperidine and4-carboxy-2,2,6,6-tetramethylpiperidine.
 4. Process according to claim3, characterized in that the light stabilizer containing at least onehindered amine unit is the compound of formula (VI)


5. Process according to one of the preceding claims, characterized inthat the composition comprises particles based on titanium dioxideintroduced before the polyamide polymerization phase.
 6. Processaccording to claim 5, characterized in that the proportion by weight ofparticles based on titanium dioxide is greater than 1% by weightrelative to the mass of the composition.
 7. Process according to eitherof claims 5 and 6, characterized in that the particles based on titaniumdioxide are coated.
 8. Process according to one of claims 4 to 7,characterized in that the light stabilizer containing at least onehindered amine unit is introduced in solution or in suspension in aliquid selected from water, caprolactam and mixtures thereof.
 9. Processaccording to one of the preceding claims, characterized in that thepolyamide is selected from polyamide 6, polyamide 6,6, and copolymersthereof.
 10. Process according to claim 8, characterized in that thepolyamide is polyamide 6,6 produced from a solution in water ofhexamethylenediammonium adipate, the process comprising a waterevaporation phase followed by a polycondensation phase, the solution orsuspension of light stabilizer containing a hindered amine beingintroduced before the evaporation step.
 11. Process according to one ofthe preceding claims, characterized in that it comprises a discontinuousprocess for producing a composition based on polyamide 6,6. 12.Composition based on polyamide obtainable by a process according to oneof the preceding claims.
 13. Composition according to claim 12,characterized in that it comprises from 0.01 to 0.04% by weight of theadditive selected from phosphorous acid and hypophosphorous acid. 14.Composition according to one of the preceding claims characterized inthat it comprises from 0.15% to 0.5% of the light stabilizer containingat least one hindered amine unit and from 0.10% to 0.30% by weight ofthe hindered phenol antioxidant.
 15. Composition according to one ofclaims 12 to 14, characterized in that it comprises particles based ontitanium dioxide.
 16. Composition according to claim 15, characterizedin that the particles based on titanium dioxide are coated.
 17. Yarns,fibres and filaments obtained by shaping a composition according to oneof claims 12 to
 16. 18. Woven, knitted, nonwoven or flocked, dyedarticles obtained from yarns, fibres and filaments according to claim 17